<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <select>
    <option value="1">北京</option>
    <option value="2">上海</option>
    <option value="3">太原</option>
    <option value="4">杨家峪</option>
  </select>
  <script>
    // select 选中 option 得到的是选中项option的value
    document.querySelector('select').addEventListener('change',function() {
      console.log(this.value)
    })
  </script>
</body>
</html>